1. Field of the Invention
The present invention relates to a light emitting device, in particular, to a light emitting device which can display an image which includes multicolors by combining light emission having different colors.
2. Description of the Related Art
A light emitting device utilizing light emitted from an electroluminescence element (a light emitting element) is a device which highly draws attention as a display device having wide view angles and low power consumption.
In recent years, in a field of developing a light emitting device, the research and development of a light emitting device capable of displaying a high quality full color image has been accelerated to ensure the market of display devices and the like for various information processing devices such as a television receiver or a car navigation system.
In order to display a full color image, it is required that regions emitting light emission of three primary colors of red (R), green (G) and blue (B) are independently provided so as to control brightness of color and chromaticity to be indicated by changing light emission time and light emission brightness in each region.
As a method for changing brightness of color and chromaticity, there is a method for changing the brightness of color and chromaticity by changing light emission time of a light emitting element, and a method for changing the brightness of color and chromaticity by changing brightness of a light emitting element. In the case of employing the former method, brightness of color and chromaticity are changed by variously combining each light emission of red, green and blue by changing light emitting time according to each luminescent color.
Meanwhile, luminous efficiency of a light emitting element differs according to a luminous body included in the light emitting element and characteristics of other substances. In a light emitting device, luminous efficiency differs in each light emitting element which indicates each luminous color. Accordingly, more current is relatively required in a light emitting element having lower luminous efficiency to obtain light emission having desired brightness.
Furthermore, the human eye has different sensitivity to each emission wavelength, and generally has higher sensitivity to the emission wavelength of green than that of red or blue. Hence, it is required to make brightness of blue and red relatively higher than that of green so that blue and red emit light to which human eye has the same sensitivity as green.
Flowing a lot of current to a light emitting element to increase brightness of the light emitting element make the light emitting element promotes the deterioration of the light emitting element, and leads to increase in electric power consumption of a display device. What is more, when emission wavelength shifts due to a deteriorated light emitting element, color reproduction of a light emitting device decreases and thus sometimes image quality is deteriorated.
Therefore, the development of a luminous body or a light emitting element which can emit light efficiently and has longer life has been attempted. For example, in Reference 1 (Japanese Patent Laid-Open No. Hei 2002-299062), it is contrived device to enhance luminous efficiency by adjusting light path length is carried out.